A Low-cost Multi-band Ground-mounted Vertical Antenna Design
By Rob L. Dey  KA2BEO  1/16/95

Specifications
Antenna description: 22' base-loaded vertical up 7'.
Center frequencies: 3.75, 7.15, 10.15, 14.2, 18.1, 21.2, 24.9, and 28.3.
Frequency range: Useable from 3.5 to 30 MHz (MUF = 31.8 Mhz) by moving coil
                 taps.
Ground radials: 2 copper wires 56' long #18 AWG 1" below ground.
                4.5' of structure is seated into the ground.
Radiator length: 22' 1" (265" or 22.08333'), 30.3 electrical degrees
                 @ 3.75 MHz. 1/2 wavelength @ 21.2 MHz.
l/d ratio: 303 average.
SWR: 1.6:1 w/o coil (Lm), 1:1 w/ coil (Lm).
Efficiency: Worst-case on 80M; 6-10% (less than 2 S-units below the signal of
            a 1/4-wave vertical).
Features
DC-grounded design eliminates static build up.
All aluminum and stainless steel construction resists corrosion, even in harsh
 environments.
Low-angle radiation pattern offers long-distance communication.
Low-cost design - only $50 using all new parts.

System Parameters

fo = 3.75 MHz
Rr = 2.94 ohms
Ca = 79.38 pf*
Xc = 534.66 ohms
Za = 2.94 - j534.66
Zo = 52 ohms
l = 265"
d = 0.875" average
h = 30.3 degrees (0.084 wavelength)
Rf = 31 ohms*
Xs = 25.5 ohms
Xp = 63.2 ohms
Ll = 24 uH
Lm = 2.68 uH (2.7 uH)
Ka = 0.965*
Km = 365.9733 ohms (Zv)
Xa = -j626.29 ohms
Cxa = 67.77 pf
w = 23561944.9

* = value estimated

Part Descriptions
1 Alum. tubing 3/4"od, 8' long, 0.050" thk (#18), insert 11" (85" exposed)
 $7.13
1 Alum. tubing 7/8"od, 8' long, insert 12", 2 slots 1-1/2" long at top (84"
 exposed) $8.13
1 Alum. tubing 1"od, 8' long, insert 13" (3/16" thru hole @ 1/2") 2 slots 2"
 long at top (96" exp.) $8.75
1 Galv. steel post (mast) 1-5/16"od, 8' long, insert 1.5' (1/4" thru holes @ 3"
 & 15") 1/4" thru hole @ 17-1/2" from top $4.53
1 Galv. steel post (ground mounting rod) 1-1/2"od (1-1/4" conduit), 6' long,
 insert 4-1/2', 1/4" thru holes @ 3" & 15" from top $3.40
2 Zinc U-bolts 4-1/2" long, for 1-1/4" dia. pipes (use on mast), Crown #383
 $1.00
1 S/S 7/8"dia. hose clamp #8, 1"max. dia. $0.59
1 S/S 1"dia. hose clamp #10, 1-1/8"max. dia. $0.59
1 S/S #10-32, 1-1/2" long bolt, with S/S: 3-flat washers, lock washer, and nut
 $0.70
1 S/S #1/4-20, 2" long bolt, with S/S: 2-flat washers, lock washer, and wing
 nut $1.34
1 S/S #1/4-20, 2" long bolt, with S/S: 3-flat washers, lock washer, and wing
 nut $1.45
1 S/S #1/4-20, 2" long bolt, with S/S: 3-flat washers, lock washer, and nut
 $0.95
4 S/S #4-40, 3/8" long screw (or use M3 x 0.5, 8mm long), with S/S: lock
 washer, and nut $0.28
1 Coil (Ll+Lm) 26.55 uH, 36 turns, #14 AWG, 8 TPI, 4.5" long, 2" dia. Q=300
 B&W #3026 $5.00
2 Copper wires 56' long #18 AWG, or use 4 Copper wires 28' long #18 AWG $0.56
1 PVC 12" long conduit, 1"id, Carlon Plus 40, grey $0.26
1 Plastic end cap (tip) 3/4"id, 1/2" long, Shepherd #9107, white $0.17
1 UHF connector, female, SO-239 $1.00
1 Right-angle bracket for SO-239 with 1/4" dia. mounting hole $2.00


A Low-cost Multi-band Ground-mounted Vertical Antenna Design
By Rob L. Dey  KA2BEO  1/16/95

Miscellaneous
Total radiator length (inches) = 96-11+96-12+96 = 265"
Average diameter (inches) = (.75+.875+1)/3 = 0.875"
Average l/d ratio = 302.857

Final Results
The antenna is mounted 31" x 31" from the corner of a 6' tall wooden fence.
Coil: 26.55 uH, 36 turns, #14 AWG, 8 TPI, 4.5" long, 2" dia. Q=300 B&W #3026

To be tested yet!

SWR: <1.5:1
BW (2:1 SWR): 400 kHz, 3.5-3.9 MHz
Coil: 46 uH 42 turns, #18 AWG, 14 TPI, 3" long, 2" dia. Q=300 #6033 ceramic
Ll = 26.2 uH tapped at 32 turns from ground end
Lm = 8.8 uH tapped at 8 turns from ground end
Note: Ll was set with a grid dip meter, and Lm was set with an RX noise bridge.
 Further "on-air tweeking" could improve the SWR and usable BW.